The possibility of colour engraving plastic components by means of a laser is of interest to the entire plastic component manufacturing industry. It is the colour laser engraving of three-dimensional moulded plastic components, for example for the automotive industry, that is of interest here. Switches, panels etc. can for example be engraved with coloured symbols. Plastic components with a coating for surface protection can also be colour engraved by means of a laser. The laser beam removes the coating layer and dye simultaneously migrates into the plastic component surface at this point. Unprotected plastic surfaces can also be colour laser engraved and subsequently coated in order to guarantee a consistently glossy appearance of the plastic components and offer protection against scratching and chemical damage. Until now such coloured symbols have for example been produced during the first manufacturing step by means of plastic injection moulding with several coloured components. The plastic components must be coated with a covering colour during a second manufacturing step. The colour layer must then be engraved by means of a laser during a third manufacturing step in order to expose the underlying plastic surface. A protective coating can optimally be applied during a fourth manufacturing step.
Alternatively transparent plastic film can be colour engraved on the back and then back-injected with a thermoplastic according to the film insert moulding method in order to obtain glossy surfaces of a consistent appearance. This method is for example disclosed as example 1 in EP-A 0691201.
On the security and/or value document market, in particular for identification documents (ID documents), there exists a requirement for the colour personalisation of these documents by means of a laser. The personalisation of ID documents consisting partially or completely of polymer film with the laser engraving method represents prior art. However, currently known methods create only images and text of various grey scales in such documents. Colour elements cannot be produced by means of laser engraving. Only in combination with prior typographically applied colour layers, which are then changed by means of a laser, is it possible to generate colour images in or on plastic components.
In recent years methods have been developed that allow the creation of colour elements in these documents which are wholly or partially made of polymer film, in particular within the area of security and/or value documents, in particular ID documents. These methods are however connected with a substantial technical effort. All methods include a printing process for realising the colour design.
WO-A 03/056507 discloses a method where a colour image can be created by means of laser engraving as follows: a colour that will react with a specific wavelength of laser light is printed onto the entire surface of a film, on the surface of which a colour image is later to be created. The reaction takes the form of a bleaching of colour pigments as soon as these are exposed to the laser. If three types of pigment are used, for example red, yellow, blue, which react a three different wavelengths, it is possible to create full-colour images in that the pigments are bleached accordingly at the laser-irradiated points. This method is however particularly tedious, as three different laser sources have to be used and the colour must be printed onto the entire surface. This means that the compound adhesion of the film will not be good enough in the area of the image following laminating.
A further method is disclosed in EP-A 2752302 and is based on the principle of a colour display: narrow lines in the base colours red, yellow, blue are printed onto film. These lines are then selectively blackened by means of a laser to create the impression of a colour image. This method is also tedious, as printing must be highly accurate in the run-up in order to create the image. The resolution of the image is also very rough, as the lines cannot fall below a distance of approx. 80 μm and the images appear dark because a large part of the image surface is blackened by the laser.
The printing of film by means of inkjet is described in JP-A 2012-011688 as a further method. For this the print motives are conventionally printed onto the film with an inkjet printer and the ink is fixed with a laser. This method is comparable to the widely used UV curing ink system. Instead of UV light a laser is simply used here to fix the ink. With this method the ink remains on the plastic surface. This method is particularly unsuitable for engraving security documents because the ink can be rubbed off the plastic surface.
JP-A 2012-011689 discloses a method and an apparatus for the colour laser printing of moulded components without damaging the substrate. With this method the ink is applied to the moulded component by means of an inkjet and this ink is then fixed on said moulded component with a laser beam.
EP-A 2179857 discloses layer constructions for ID card to be written on by means of laser engraving, which have an additional layer that is applied to the card body following said laser engraving and limit or completely prevent subsequent writing on the card by means of laser engraving and therefore the forging of existing information. Colour laser engraving is not disclosed.
WO-A 2005/033218 discloses coating compositions containing iron blue pigment, which are suitable for producing a laser engravable coating layer that can be laser engraved in a way that is powder- and residue-free with a laser. The coating layer is removed and corresponding information applied by means of laser engraving here.
It is therefore the task of the present invention to provide an improved and simple method for the partial dyeing, in particular for the colour laser engraving of plastic components, preferably of thermoplastic plastic components, more preferably of plastic film and/or film layer compounds.